1. Field of the Invention
The present invention relates to a method of and an apparatus for transferring a substrate from a take-up position to a specified position.
2. Description of the Related Art
In the manufacture of, for example, liquid crystal displays, a plurality of glass substrates used for manufacturing liquid crystal displays are stored in a cassette in a stacked manner and are conveyed to any one of manufacturing units by the cassette.
Each of the manufacturing units has a transferring apparatus and a processing section. The transferring apparatus is designed to transfer the glass substrates, one by one, form the cassette to the processing section. The transferring apparatus comprises a cassette mount region on which the transported cassette is placed so that the glass substrates in the cassette are located at a predetermined take-up position, and transferring means for taking out the glass substrates, one by one, from the cassette on the cassette mount region and transferring it to a specified transfer position which is suitable to the processing section.
Generally, the cassette is large enough to allow each glass substrate to move into and out of the cassette, with its sides not contacting the inner walls of the cassette, even if the transferring means moves sideways while transferring the substrate from the cassette. Thus, each glass substrate in the cassette may be displaced when the cassette is vibrated or inclined while the cassette is being moved from one manufacturing unit to another.
The transferring means moves between two fixed positions, that is, between the take-up position and the transfer position and transfers the glass substrate along a fixed path. Therefore, if a glass substrate is stored in the cassette with being displaced from a predetermined take-up position, this glass substrate is transferred by the transferring means from the cassette to the transfer position while maintaining the displaced state. Accordingly, the transferred glass substrate is located at a position displaced from the specified transfer position.
In order to solve the above-mentioned problem, there is provided a transferring apparatus which has a positioning mechanism for setting glass substrates in a desired position in a cassette placed on the cassette mount region.- The mechanism has two pairs of positioning plates, each pair of which opposes each other. The positioning plates are moved toward the center of the glass substrate from outside so as to force the side edges of the substrate, thereby positioning the substrate in the desired take-up position. By positioning the glass substrate at the take-up position, the substrate can be accurately transferred to the transfer position.
However, the positioning mechanism applies an impact to the glass substrate since the plates mechanically push the four side edges of the glass substrate stored in the cassette. Applied with an impact, the glass substrate may have micro-cracks or may be chipped. Particularly, when the thickness of the glass substrate is smaller than 1 mm, micro-cracks increases.
Here arise two problems. First, dust is generated when micro-cracks are made in the glass substrate or when the glass substrate is chipped. The dust causes decrease in the yield of the manufacturing of the liquid crystal displays. Second, thermal stress concentrates at the micro-cracks or at a chipped part when the glass substrate is heated and cooled in another manufacturing processes, and the substrate may be broken.
If glass substrates repeatedly receive impacts, each time at the transferring apparatus of each manufacturing unit, they may therefore be broken at last, even if they have no micro-cracks or chipped parts at all.
The present invention has been contrived in consideration of the above circumstances, and its object is to provide a method and apparatus for transferring a substrate from a take-up position to a second position, positioning it in a desired manner at the second position without making micro-cracks in the substrate or chipping the substrate.
According to the present invention, there is provided a method of transferring a rectangular substrate from a first position to a second position by substrate-transferring means, which comprises the steps of: detecting at least two points on one side of the substrate located at the first position by non-contact manner and generating detection signals; generating positional data in accordance with the detection signals, the positional data representing an angle at which the one side of the substrate inclines to the transferring means and a distance for which the one side of the substrate is displaced along a line extending at right angles to the one side; and transferring the substrate from the first position to the second position and to position the substrate at the second position by the transferring means while controlling the transferring means in accordance with the positional data.
According to the present invention, there is provided an apparatus for transferring a rectangular substrate from a first position to a second position, which comprises: transferring means for transferring the substrate from the first position to the second position; detecting means for detecting at least two points on one side of the substrate in non-contact manner, and generating detection signals; and control means for generating positional data in accordance with the detection signals, the positional data representing an angle at which the one side of the substrate inclines to the transferring means and a distance for which the substrate is displaced in a direction extending at right angles to the one side of the substrate, and for controlling the transferring means in accordance with the positional data to transfer the substrate from the first position to the second position and to position the substrate at the second position.
In the method and apparatus according to this invention, the detecting means detects at least two points on one side of the substrate and generating detection signals representing the points detected, and the control means generates the positional data from the detection signals. The positional data represents the angle at which the one side of the substrate inclines and the distance for which the substrate is displaced in a direction extending at right angles to the one side of the substrate. The control means then controls the transferring means in accordance with the positional data. Thus controlled, the transferring means transfers the substrate from the first position to the second position and to position the substrate at the second position.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.